Radio frequency amplifier



Feb. 16, 1960 H. SCHARLANIELSEN ETAL RADIO FREQUENCY AMPLIFIERFiledSept. 12, 1957 E 5 mm m% n 5. m m W M v m AJR m T L c A non A L.mmo

v mwm B f" F w??? v 3 a c'apacitairi'celbetweeil One side: of 'thee ohei 1 I line and'the chassis' 'Acro's's this capacitance. is connected I YV 7 2,925,477 a'fvariable" trimmer "condenser. The values: of capacity;andjinductanceija're"selected to resonate withthe tube; RADIO inputcapacity, and thejtapping point for the one line .is

. Hans Scharla-Nie'lsen, Indiaiantic, andlDaniel DgM cRae. so'fselectedthat voltage step-up occurs.

stiofa U-shaned and Floyd Donald J. McLamh, Melbourne, Fla;,structurally, the inp'uttahk may consi #8 5 Radiation, n rm a 6 1mmetallic device, having one longer. leg and. one shorter tron of Floridar leg. The ha'se of the'u provide s a short atithe cold end temher 12,1957, S e of the tanl i circuit, and the openend of th'elong legconnected to the grid .of' the ampl fier. The shortleg s extendedparallelto and is spaced from the chassis bya stripof insulationl Thestructureis rigidfbyfvirtue of I theintinia'te'relation between theshort leg and the chassis, i.

7 and maybe 'ruggedhy virtue of fabrication from a solid amplifiers, andparticularly to';'ultra-high frequencyffq mp" .blockoffmetal, inwhich alongitudinal slot is milled. 1 p fi v n novel input a butpiit n f fi ySince'the bar may he bolted solidly to the chassis while tions andcoup-ling elements, l l ,I

rernaining electricallyor. conductively isolated therefrom,

. A"va 'i ty f amplifiers are k to t e n t a t. t hes't rncture is 'wellsuited to withstand shock and vibra- Whibh are ap b 0f operating in Q-FQ QQQWfi tion, While the capacity of the bar to chassis forms aSpecifically in the i y of 0 lf l capacity which assists in tuningtheinput tank. I I i i amplifiers have'been relatively v ce t. loy Themajor impedance determining element of theitank, eiiiciency, incapableof operatiOn 0Y d va 'fil Q i.el,.the1line' formed by the long and shortlegs, may environmental c n i i n having v y. mal m be made to have avery high ance the. bar has. ex-. power, and small power gain. b tremelylow resistance. 'The loading effects of the tuning v Application Sep 119, Claims. 01; mp5s 'lihepre sent' invention relates generallytoivaeuumtube It is a broad object of the present invention to provide 7 lcapacitor d h g id bi i i y appear acrqss m anovel amp fi tunable. Ovfflrange, of frieqlielmis n" lower. line, i.e;, the line formed by theshorter leg and k* band, capable Operation. fr m ,a riv the chassis, andhence do not affect the Q,- and therefore of [convenient impedance, andof relatively low power and the voltage. step-upbf the main .6; upperlin I i voltage output, which shall have high powergain'fand The butputtank circuit is attuned transmission line, efliciency, be Small,ruggediz d, and capable Of Ofifle consisting of a metallic tube,extending parallel with the 7 tion fi Severe QllViIOnmemal iO T I echassis of the, system -and a'short distance therefrom so Specific dimnt 'fi lilififi j tim astoiforr'nther'ewith a'capacitively loaded Awaveline; t the present v n m .0 watts t p i p vr s]. The Itubelis'coupled' togthe amplifiertube by means of delivered by a single tube'to"a 5 0 ohm lofadl 'h from. a two watt, '50 olJn,B..E. fosci11atpr ,Ic n fai na a ohm' driver. Since Tfa'rf g I signal is required foriclass'C eperatiorigi tojemploy voltagestep uplin the input. circui feature ofthe present invention to.provid ,toLD.C; oltage, andhence need have onlysufiic'ient ratfor drivingafhlgh efiicieiic fa:- 'plfiertub'jhavihgffela in'gItfo' Withstand the R'.F.. voltage tol'the; outputtank. tively high inputicapacitance, athig'h' level, rom a low Q Itlis:TacboIdingI'y, abroad object e f the resentinvenlevel 'signal'sou'rce.'1 I v Zi o .5 'ad f q ue icitmm v A further problem encounteifed'infthelper'tinenta I high power galhand igh efiiciency of convenientinput; todesign an output tank for an amplifier withf eda ce nd'cai5ab1eof drivingian output lqadof Can-.1 ciently high Qto realizea.high.power.gain,.,bf the i I v v of 2,'fwhich is yet capable of.efficiently cphpling" about,v

' 50,.watts0fpowerfto a SOohin load,'the.circnitryl to berugg'ed and tob tunable ever-111e, dsiie'd r'equ range. jIt' i's'aj furtherjfeaturelofi the .inventio r the required output"circuiti'y-.and a An input tankcircuit according". o'the, prese t H'VQH? v'i tibnconsistsof ewetransmission lines, arranged thatv theirseries combination as seen trom'1 v amplifiertube isthe .conjugateiof npu I f the inyntipnto. provide: anovel mphfienh ving 'a tuned transmission lin'ege. tunednsmission;linepntputtanlg the i eiiin i t s e y 4 'tanlg hei'n'"employdtogprh'; -Q- ev 1, as. a sol t ng to the vacuum tube anode.

The above and still further objects, features and advantages of thepresent invention will become apparent- 5 upon consideration of thefollowing detailed description of one specific embodiment thereof,especially when taken inconjunction with the accompanying drawings,wherein:

The single figure of the drawings is a representation, partly schematicand partly structural of an amplifier ac-. l cording to the presentinvention.

Referring now more particularly to the accompanying drawings, thereference letter T denotes a tetrode vacuum tube, preferably of the4CX300A Eimac stacked-ceramic type, although other tubetypes maybeemployed within the scope of the invention. The tetrode T includesacathode 1, a control grid 2, a' screen grid 3, an ar'iode' 4 and a heatradiator 5, which is of -metallic structure and is secured electricallyand physically at multiple points about the anode 5, the anode and" theradiator being cylindrical in shape.

Surrounding the radiator 5 is a layer 7 of Teflon or the like, whichconstitutes a suitable low loss insulating medium for a clamp 8, in theform of a ring surrounding the radiator 5 and insulated therefrom forDC. The radiator 5, the layer of Teflon or the like 7, and the clamp 8form a capacitor for coupling an external tank circuit to the anode'4. v

The numeral 10 denotes the chassisof" an amplifier structure. Extendingadjacent and parallel thereto is a metallic tube 11, the length ofwhich,in relation to its spacingfrom chassis 10 established a parallelresonant circuit, in the form of a capacitively loaded quarter wavetransmission line shorted at one end.

An anode power lead 12 extends internally'of the tube 11, from a powerterminal 13 to anode 5, ininsulated relation to the tube 11. Thelatteris connected at oneend to the clamp 8, by ;a short lead L,.and isthereby cap'acitively-coupled to the anodex4. The termimal 13 may beby-passed to ground for R.F. by a fixed condenser 14, and the tube 11may be shunted to ground by a variable tuning capacitor 15, which servesto vary the"-resonant frequency of the'output tank" circuit overa=smalllrange of values. I j" i Since the tube 11 is D.C. isolated fromthe anode; the tuning'capacitor 15 need only bedesighed for with}standingRF. voltage, and not R.F. superposed on D .C.; The lead 12 inconjunction with the tube 11 providea" concentric line R.F. shorted atboth ends. f

Output power referenced to the chassis potential may be' derived fromthe outside of tube 11, by means of a" tap 16, and a conductive lead,since tube 11 isD.C. connected to the chassis; Moreover, the tap pointmay be selected to provide an impedance match to a ohm or other desiredload, since the tube 11 and the tap 16 act as an impedance step-downtransformer, while the tube itself is seen from the tube anode as a'highimpedance equivalent to a parallel resonant'circuit.

The tube 11 may be bent into semi-circular, or circular form, orotherwise as desired, to "conserve space; 0 The input tank circuitconsists of a U-shaped bar '20, whichmay be machined from a soliclblockof rnetal. The" U-shaped bar 20 includes a relatively'longileg 21;a:relatively short leg 22 extendingparallel to the longf leg 21, and abase 23 joining the legsjat' an end/The bar then constitutes a parallelconductor'transmission line openat one end, and shorted bythe' base23"attthe Y otherend." Theopen end 24 of the long 1eg 21 is"- directlycon-" nected to the grid 2, while a point '25 of the l'ong leg21,-:adjacent to but'not at the base 23, is-cupled by a caPacitor'26toasi'g'nal input t'erminal 27. 5

The short -leg"22 is firmlyse'c'ured to-th a s ll?" h i llwextendingparallel-thereto; hurt el'ee' callyinsulatedtirerefrom' -h' 'r alayer-28- of Tefleng- -or other 7 5 herent capacity. For the preferredtube type this value is about 40 #pf. The overall lengths of the inputtank lines, i.e., legs 21 and 22, and their spacings and characteristicimpedances, are selected to resonate with the tube input capacity, theleg 21 being for this purpose shorter than Mr A, where A is theoperating wave length, and hence appearing as an efiectiveinductance.

The transmission line 20 represents an extremely high Q circuit, becausefabricated of thick low resistivity metal, and because lacking inloading of any type; It follows that a tremendous gain in R4F. voltageappears, as between tap 25 and grid 2. It has been found, in practice,that two watts can be supplied from a 50 ohm source, at terminal 27, andthat this power is sufiicient to develop adequate R.F. driving voltageat the grid of the amplifier despite the fact that the amplifier isoperating class C, or nearly class C, in order to obtain high efficiencyof power conversion on the output circuit. In effect the control grid ofthe tetrode 1 sees an impedance conjugate to its own impedance, whenlooking into the line 20, and hence forms part of a series resonantnetwork, which permits high R.F. driving currentto flow. At the sametime the input terminal 27' s'es'SO ohms byvirtue of the tap point 25,and the line 20 provides a high voltage at the grid because it is openat the grid end and is a high Q line. An impedance match exists bothbetween the driving source and the tank circuit, and between the tankcircuit. and the tube input circuit, accordingly, accompanied by avoltage step-up at the tube input circuit Fixed bias forflthecontrolrgrid is provided from a negative voltage terminal 40, which isconnected via choke 41, and two series connected resistances 4 2, 43 tothe base 23. 'In addition, a parallel resistancer45 and condenser 46 isconnected from the junction of resistances 42, 43 to ground. The latterelement provides grid leak bias, and is suitably designed for thatpurpose. mayberemoved whenthe amplifier is in operation, but

. is required whileianode and screen voltages are applied withoutconcurrent application of RF. drive voltage.

Theiscree'n grid 3 is connected directly to a B+ volt"- a'g'e terminal47, and is by-passed to ground by a condenser 48, which in apreferredrembodiment of the invention may be'built into the socket ofthe tube 1.

The two transmission line tank circuits, i.e., the input,

tank and the output tank, may be physically located on oppositesides ofa chassis wall, to reduce coupling therebetween.

While the system ofthe invention has been disclosed as an amplifier, thestructure and circuitry areequally adapted to utilization as anoscillator, by coupling the output lead to the input lead in properphase, and may beemployed as'a modulated amplifier, as by varying the.anode voltage in response to a signal.

v While We have described and illustrated one specific embodiment of ourinvention, it will be clearthatvariationsof the details of constructionwhich are specifically illustrated and describedmay be resorted towithout de 1 parting from thetrue spirit and scope of the invention "lasdefined in thezappended claims; 1 What claimedis: a

tank circuit comprising a metallic chassis at ground potential, a'U-shaped metallic structure having" a relatively long 'arm, a relativelyshort arm' 'parallelfwith" andspaced from-said long 'arm' and afl'shortcircuitingi element: joining said arins-onlyat adjaccnfends -thereof?The lower leg 22 taken The fixed bias the remaining end of said longar'm being open, an insulating 'sheet located between said short arm andsaid metalllc chassis and means mechanically and insulatedly securingsaid short arm to said chassis, COHHCCilOllSLfOI' applying drivingsignal between said sho'rt-circuiting element and an intermediate pointof said long arm, and

of said relatively-short arm and its insulated relation to said chassis.V

3. In combination, a vacuum tube amplifier having an operatingfrequency, said tube having a grid and a cathode, the grid and cathodedisplaying predetermined capacitance therebetween, a two conductortransmission line open at one end and short circuited at the other, anextensive metallic structure, one of said two conduc tors beingproximately spaced from said extensive metallic structure along itslength by an' insulating strip and providing distributed capacity by.virtue of the proximate spacing and its length, a connection from saidgrid to a point adjacent the open end of said transmission line at theother of said conductors, adriving' circuit coupled to the other of saidconductorsintermediate the ends of said transmission line,said'twoconductor transmission line having an electrical length suchthat it is elfectively an inductance, said inductance and capacityarranged and selected to have a net inductance in series which resonateswith the predetermined capacitauce at said operating frequency." a

4. The combination 'accordingftoiclaim 3 whereinfls provided a variabletrimmer condenser forflvarying saidj capacity, said trimmer capacitybeing corinectedacrjoss 7 :said capacity. a

voltage appears across said capacitance than'isavailable from saiddriver. a

5. The combination according claim 4whei'ein the said tuned circuit, adistributed inductive reactance in series with a distributed capacitivereactance as another element of said tuned circuit, said inductivereactance and capacitive reactance in series having anet inductivereactance and means connecting "said driver across a portion of saidfirstmentioned inductive reactance point of coupling of "said trimmercondenser is imme- I diately adjacent the shorted end of saidtransmissionline. r Y

cuit including said capacitance as a series'element of such that voltagestep-up occurs by virtue of auto-trans former action in said firstmentioned inductive reactance,v said tuned'circuit being series-tunedto' said wavelength, i and having a relatively high Q, whereby a farhigher;

2,090,513 Farnham Aug. '17, 1937 2,228,862 "Wessels Jan. 14, 19412,272,351 Ramsey Feb. 10, 1942 2,278,238 Buschbeck Mar. 31, 1942 I I2,421,784 Haeseler et a1, June 10,1947 I 2,463.,724- Stamer- .L.. Mar.8, 1949 2,481,456 Ty zzer Sept. 6, '1949 2,554,457 'Dome ;l May 22, 19512,562,921 Kandoian Aug. 7, l 2,665,339 Leng Ian. 5, 1954 2,717,363Hubbard .Q Sept. 6, 1955 2,748,286 Bussard L May 29, 1956 2,763,843 ICushman Sept. 18, 1956 2,765,444, Green Oct. 2, 1956 2,766,383v HubbardOct. 9, 1956 2,772,355. 'Deutsch et al.- Nov. 27, 1956,

FOREIGN PATENTS -,7 47,904' 'G ermany OCL20, 1944 7 The combinationaccordingto claim 6 wherein said I portion, of s'aidinductive reactanceis selected to pro I vide a substantial'impedance match with saiddriver. r

8'. Thecombination according to claim 7 wherein said "inductivereactance 'isconnected withjan auxiliary tuning" capacitance.

9. The combination according to claim 7 wherein said inductive reactanceincludes a section of transmission line having a length less than 4 anopen output end and its remaining end short-'circuited, said open outputend being connected to saidinput capacitance.

10. A vacuum tube circuit operating at a predetermined frequencyincluding a vacuum tube having an anode, a control grid, and a cathode,means connecting said cathode to a point of reference, potential, a i

grid tank circuit comprising a transmission line open at oneend andincluding a first conductor, a second conductor extending substantiallyparallel to said first conductor, 'a short circuit between two adjacentends of said first and second conductors, a third grounded extensiveconductor extending parallel to and adjacent to and insulated from saidsecond conductor at least along the entire length of the latter, thegrid to cathode circuit of said vacuum tube having substantial inherentcapacity, said first and second conductors constituting an inductance byvirtue of their length at said predetermined frequency and said shortcircuit, said second and third conductors constituting a capacity byvirtue of their lengths and their insulated relation, said inductanceand capacity providinga net inductance resonating with said substantialinherent capacity at said predetermined frequency, the funshorted end'of said first conductor being connected-directly to said control grid,wherein is provided an-input driving terminal, and means coupling saidinput driving terminal to'a point of said first con-; 7 ductor morenearly adjacent to, said short circuit than 40 toathe open end'offsaidfirst conductor.

i "hesitate eaai iaae me r thapae NITED STATES PATENTS"

